Keys are positioned on a mobile information device, such as a cellular telephone, in order that a user can select functions and input text such as numbers and letters. The user can perform an operation by pressing one of the keys using a finger, thus causing the mobile information device to execute processing of a desired function or input.
Recent years have seen an appearance of mobile information devices that are operable by small amounts of force, or even just by touch, through configurations such as where the keys are capacitive touch sensors. Although mobile information devices of the type described above have an advantage of touch operations being easy to perform, a problem is that erroneous inputs that are not intended by the user also easily occur.
Patent Literature 1 recites a mobile information device that prevents unintended touch operations (erroneous inputs) occurring when a face of a user makes contact with touch sensor type keys during a telephone call. Erroneous inputs are prevented by positioning a touch sensor adjacent to a receiver of the mobile information device so that, when an ear of the user contacts with the touch sensor, input via the keys is disabled.